Vertical form fill and seal continuous pouch machines are known in the art. Generally, they receive a continuous film and form the film into a film tube about a forming tube. The forming tube typically has a circular cross section, although other cross sections have been used.
The film is continuously fed around the forming tube and sealed vertically to form the film tube. The vertical seal is typically a lap seal or a fin seal.
Forming tubes can include ploughs or tucker bars to from creases that can be used to form gussets, to make stand-up pouches. The plough or tucker bar applies tension in an inward direction creasing the film tube. Forming plates may be provided on either side of the plough, applying tension in an outward direction. Two ploughs centered about a single tucker bar will form a “W” shaped gusset. The ploughs and tucker bars may be fixed in one location, such as at the bottom of the forming tube, or moveable in any direction. Examples of a tucker bar and forming plates may be seen in U.S. Pat. No. 6,679,034, hereby incorporated by reference. Tucker bars (and forming plates) may be used on a single side of the bag, forming one gusset, or on opposing sides, forming two gussets. Forming tube assemblies may be changed out to form bags of other sizes. Another prior art machine is shown in U.S. Pat. No. 6,691,491, hereby incorporated by reference.
After the film tube passes the forming tube and tucker bar(s) it moves vertically downward to a sealing zone. Seal bars intermittently create a horizontal seal. The seal bars may be rotary, and can be in pairs to increase machine speed. An example of seal bars is given in U.S. Pat. No. 6,519,922, hereby incorporated by reference.
The horizontal seal forms the top seal of the pouch below the seal, and the bottom of the pouch above the seal. After the seal is formed a scale or other input device drops a predetermined amount of product through the forming tube. At the same time the film tube is advancing downward. When the subsequent seal is formed the product is below the sealing zone. The seal is formed, forming the top seal of the filled bag and the bottom seal of the bag above, thus sealing the product into the bag. Stripper bars, such as those shown in U.S. Pat. No. 6,519,922 may be used to help ensure the product is below the sealing zone when the seal is made.
There are other type of vertical bag machines that make other types of bags. For example, pillow bags are common. Other bag designs require other configurations of the vertical machine. It is desirable to change a production line from one type bag to another. This typically involved removing the forming tube and the horizontal seal assembly. A new forming tube is installed, and the seal assembly is rotated, then reinstalled. The changeover, particularly removing the horizontal seal assembly, can be lengthy, which is, of course, undesirable. Accordingly, a vertical form fill and seal continuous pouch machine that can readily be converted to make other style bags without removing the horizontal seal assembly is desirable.
Some pouches are made on a horizontal pouch machine. Horizontal machines are generally slower, but provide advantages, such as the ability to place zippers or other reclosable devices on the pouch. Zippers (as used herein zipper includes other reclosable devices) are difficult to provide on vertical form fill and seal continuous pouch machine because the zipper would be added vertically at the forming tube (for example where the vertical seal is made). However, the horizontal seal must seal the entire width, thus requiring sealing through the zipper. It is difficult to effectively seal through a zipper. Accordingly, a vertical form fill and seal continuous pouch machine that provides a zipper or reclosable device is desirable.
The length the product drops can affect the quality of the filled pouch. A lengthy drop can cause breakage if the product is weighty. Also, the product tends to spread out vertically as it drops, and a lengthy drop can increase the vertical spread. If the vertical spread is too great, the product can get caught in the seal, or get caught above the seal, and thus not fully filling the intended pouch. The drop length along the forming tube is dictated by the required height of the forming tube. The drop length from the forming tube to the seal zone is dependent on the width of the tube in the direction perpendicular to the horizontal seal direction. The film tube width must change from the width of the forming tube at the exit of the forming tube to zero at the seal zone, without stretching, tearing or deforming the film. Thus, the tube-seal drop length must be long enough to allow for a gradual transition in film tube width. Accordingly, a vertical form fill and seal continuous pouch machine that provides a short tube-seal drop length, yet allows for the needed transition to zero film tube width, is desirable.
Some prior art vertical form fill and seal machines use an non-circular forming tube with a long and a short axis. Such tubes are typically disposed with the long axis parallel to the cross-direction and the horizontal seal is formed perpendicular to the cross direction. While this has been necessary for certain designs, it unfortunately results in a transition from the film tube width being the long axis to zero, and a resulting long drop length. Accordingly, a vertical form fill and seal continuous pouch machine with the horizontal seal being perpendicular to the short axis of the forming tube is desirable.
Prior art film used in vertical form fill and seal continuous pouch machines is typically a laminate to accommodate various needs, such as printing graphics, sealing, and to provide a barrier for food freshness and/or and food safety. The inner surface of the film tube is a material that will seal to itself with heat, such as OPP or PET. A gusseted pouch formed with a “W” has 4 layers of film (each corresponding to a segment forming the “W”). Each segment has an inner and an outer surface. All four layers are typically sealed to one another. The two outside segments have the inner surface facing the inner surface of the inside segments. Thus, the two outer segments will seal to the two inner segments. However, the two inner segments have an outside surface facing one another. Thus, the inner segments do not seal to one another. The prior art overcame this problem by applying a coating that seals to the outer surface in certain locations. This allowed all four segments to be sealed, but added cost. Accordingly, a vertical form fill and seal continuous pouch machine that seals a gusset without a need for coating the outer surface is desirable.
One problem with forming the gusset is the film can be difficult to crease without damaging the film. Accordingly, a vertical form fill and seal continuous pouch machine that provides for creasing the film without damaging it is desirable.